Conventionally, as a technique relating to a spark plug having a noble metal tip at the front end of a ground electrode, for example, the technique disclosed in JP-A-2005-251727 is known. In this technique, the ground electrode is welded to one end surface and the inner circumferential surface of a metal shell in a state in which an end surface in the lateral direction is exposed.
In the technique of the related art, since the end surface of the ground electrode in the lateral direction is in a state of being exposed to the outside, it is difficult to configure an inner layer mainly including copper in the ground electrode. This is because the operation environment of the ground electrode is at a high temperature, and, when the ground electrode is formed in a state in which the inner layer mainly including copper with a low melting point is exposed to the outside, there is a concern that the copper may be melted due to combustion heat, and the ground electrode may be deformed or detached. In addition, in the technique of the related art, even when the inner layer is formed in the ground electrode, since the inner layer moved into a state of being exposed to the outside, it is not possible to sufficiently improve the heat conduction capability of the tip. This is because copper configuring the inner layer is directly joined to the metal shell so that the heat conduction capability of the tip is improved. As described above, in the technique of the related art, there are problems in that the thermal conductivity of the ground electrode is small, and the heat conduction capability of the tip provided in the ground electrode is not sufficient.